This experimental method was obtained from the official website of the Fourth Military Medical University

Operation method

Experiments for the determination of total acidity of fruits

Principle

Fruits are rich in organic acids, such as acetic acid, citric acid, malic acid, tartaric acid, etc. These organic acids can be titrated with a standard solution of alkali, using phenolphthalein as an indicator. According to the alkali concentration and volume consumed, you can find out the total acidity in the fruit: organic acid % = CNaOH-VNaOH K/Mx × 100% where: Mx for the actual titration of the sample volume (g); VNaOH for the titration of the fruit itself consumed by the amount of NaOH standard solution (ml); CNaOH for the titration of the fruit of the concentration of NaOH (mol / L); K for the basic unit of organic acids formula amount MB × 10-3, the value of which refer to the following table to analyze citrus fruits of the Brassicaceae family and berries of the lingonberry family according to citric acid. When analyzing fruits, drupes and most of the berries are calculated according to malic acid. Because of the low acid value in the fruit, the deionized water used should be used as a blank experiment.

Materials and Instruments

Fruit samples
NaOH solid Phenolphthalein indicator
Electronic balance Alkaline burette Conical flask Homogenizer 250 ml volumetric flask Beaker Filtering device Pipette.

Move

1. Take sweet orange, remove the skin to remove the membrane to remove the core, the remaining part in the mortar, mashed, weighed into a paste made of pulp about 20g (quasi to two decimal places) in a clean and dry beaker, filtered through gauze to a small conical flask, and then squeezed the gauze dry, and then filtered through cotton to get the juice. The juice was fixed in a 250mL volumetric flask and shaken well. Pipette 25.00 ml of filtrate in a conical flask, add 1~2 drops of phenolphthalein indicator, titrate with NaOH standard solution (V) to the end point (pink, and 0.5min without fading). Determine 2~3 times in parallel.

2. Another 25.00mL of deionized water was pipetted and titrated to the phenolphthalein endpoint with NaOH standard solution. Determine 2~3 times in parallel.

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